Fluid delivery system and flow control therefor

ABSTRACT

A fluid delivery system having a closed-loop control process for delivering a medical fluid to a patient. A fluid infusion system includes a pump for delivering a fluid to a patient via an administration tube. A flow sensor associated with the administration tube provides an indication of the actual flow rate of fluid in the administration tube. Such a flow sensor may comprise a positive displacement flow sensor constructed using micro-fabrication and/or micro-molding techniques. A reader reads the actual flow rate signal and provides an indication to a controller for controlling the pump. The flow rate information can also be used for providing status information, such as the existence of a blockage in the fluid delivery system.

PRIORITY CLAIM

This patent application is a continuation of U.S. application Ser. No.11/333,594, filed on Jan. 17, 2006 now U.S. Pat. No. 7,879,025, which isa continuation of U.S. application Ser. No. 10/177,544, filed on Jun.21, 2002 (now abandoned), the entire disclosure of which is incorporatedherein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to delivering fluids to a patient and,particularly, to closed-loop flow control systems and methods fordelivering medical fluids to a patient at a controlled delivery rate.

2. Description of the Prior Art

A variety of fluid delivery systems are currently being used in themedical field for delivering medical fluids (containing medication,nutrition, saline, and so on) to human and veterinary patients. It isoften desirable to administer such medical fluids at relatively precisedelivery rates. In some cases, the rate of delivery may be exceptionallyimportant. In recent years, it has also been found to be advantageous touse various types of infusion pumps to administer medical fluidsautomatically, over extended periods of time. A typical infusion pumpdelivers the medical fluid into the patient's venous system using adelivery channel which usually comprises an administration tube (e.g., apolyvinyl chloride tube) connected to the patient using some form ofcatheter, needle, or the like.

Heretofore, infusion pumps and similar devices known in the art havetypically not provided closed-loop flow control to achieve precisedelivery rates. Rather, flow control has been open loop because actualflow rate information has not been used in controlling the infusionpump. A typical accuracy of such systems, in terms of flow rate, isnormally no better than about +/−5%, and requires relativelysophisticated (and costly) mechanical components and tightmaterial/geometry controls (e.g., of the tubing) to achieve that rate.In fact, ambulatory pumps typically achieve accuracies of +/−6-8%.Further, non-ambulatory pumps often do not achieve a five percentaccuracy range at low flow rates or over longer time periods due tomodification of the tubing material over time. For example, a typicalperistaltic type pump requires repeated deformation of theadministration tube. This deformation process changes the elasticrecovery properties of the tube, resulting in changes in the volumetricoutput of the pump over time. One volumetric pump available from theassignee of the present application has a specified rating of +/−5% at1-1200 ml/hr and +/−10% at 0.1-1 ml/hr. Another pump available from theassignee of the present application has a rated accuracy of +/−5% forthe first 24 hours of use and +/10% thereafter.

While the foregoing accuracy ranges may be acceptable for some uses,greater accuracy is desirable for other uses. In some prior art systems,the pumping mechanism associated with the infusion pump is monitored andcontrolled, but the actual flow of fluid in the administration tube isnot. For example, commonly assigned U.S. Pat. No. 5,533,981 describes asyringe infusion pump having a sensor for detecting the position andcapture of a syringe plunger for use in controlling the dispensing offluid from the syringe. Commonly assigned U.S. Pat. No. 6,078,273discloses a variety of known infusion pump systems such as, for example,roller pump systems, peristaltic-type systems, valve-type systems, andmotor driven systems. Further, commonly assigned U.S. Pat. No. 5,482,841discloses a volumetric-type infusion pump. An example of an ambulatoryinfusion pump is a pump sold under the mark IPUMP by the assignee of thepresent application. An example of an ambulatory pump may also be foundin U.S. Pat. No. 5,993,420.

Some systems have attempted to provide closed-loop control. For example,commonly assigned U.S. Pat. No. 5,533,412 discloses a pulsed thermalflow sensor. In such a system, the fluid is heated by a pulsed heatingelement. The fluid carries the thermal pulse through a flow channel totwo sensor elements spaced apart, downstream from the heating element.The transit time of the thermal pulse between the two sensor elementsprovides an indication of the fluid flow velocity. Thus, such anapproach requires the application of a heat pulse to the fluid in orderto determine flow rate information.

Other prior art systems use information generated by positional encodersand decoders associated with a motor shaft to control an infusion pump.For example, the above-mentioned U.S. Pat. No. 6,078,273 discloses anencoder/decoder for use in controlling a medical infusion pump. Whilesuch systems reflect improvements in the art, they do not control fluiddelivery in view of actual flow rates. In some circumstances, therefore,such systems would not provide as accurate information and tight controlbased on actual fluid flow rate data.

Sensors, such as positive displacement (PD) flow rate sensors, have beenin use for many years and directly detect flow rates. A typical PDsensor includes two complementary rotating elements that, when exposedto a fluid flow, allow a relatively well-defined volume of the fluid totransfer from one side of the sensor to another side of the sensor witheach rotation (or partial rotation) of the rotating elements. Oneadvantage of PD sensors is that they support a variety of fluids withsubstantially equal levels of accuracy. In the prior art, such devicestypically measure large fluid flow rates and the requisite level ofprecision is achieved by conventional precision machining and polishingtechniques. In fact, components must sometimes be matched to ensureminimal clearances of the rotating elements and inner housing geometry.Such conventional PD sensors, however, are not well-suited for use inhigh-precision medical fluid delivery systems. For example, a commercialinfusion pump may require the ability to deliver fluids over a widerange of delivery rates (e.g., 4 logs), including very low flow rates.Moreover, conventional manufacturing techniques tend to be expensiveand, therefore, are not well-suited for use in manufacturing disposableitems.

In recent years, fabrication techniques have developed that allow forthe manufacture of micro-fabricated devices. Some of such devices arereferred to as micro electro-mechanical system (MEMS) devices and micromolded devices. One technique for fabricating such devices is referredto in the art as LIGA processing. LIGA (Lithographie GalvanoformungAbormung) was developed in Germany in the late 1980s and translatesroughly to the steps of lithography, electroplating, and replication.LIGA allows for the formation of relatively small, high aspect ratiocomponents. Using this technique, a photoresist layer (e.g., an acrylicpolymer such as polymethyl methacrylate (PMMA)) is applied to ametallized substrate material. The photoresist layer is selectivelyexposed to synchrotron radiation (high-energy X-ray radiation) via amask pattern to form the desired high aspect ratio walls. Thus, theradiation “unzips” the PMMA backbone. The exposed sample is thereafterplaced in a developing solution that selectively removes the exposedareas of PMMA. One development solution is 20% by volume of tetrahydro1,4-oxazine, 5% by volume 2-aminoethanol-1, 60% by volume2-(2-butoxyethoxy)ethanol, and 15% by volume water. The sample isthereafter electroplated; metal fills the gaps within the PMMA to form anegative image. The PMMA is then removed using a solvent, leaving ametal form for either immediate use or for use as a replication master.The entire LIGA process is described in greater detail in chapter 6,page 341 of Marc Madou, “The Fundamentals of Microfabrication, theScience of Miniaturization,” Second Edition (CRC Press 2001).

LIGA has been identified for use in manufacturing micro-fabricated fluidpumps. It is believed, however, that LIGA-based micropumps have neverbeen made available commercially. Cost is one substantial drawback ofLIGA; it is believed that there are relatively few synchrotron devices(e.g., 10-15 devices) in the world. Accordingly, LIGA is fairly limitedin its applicability for directly manufacturing low cost devices.

In view of the foregoing, an improved system and method for delivering afluid to a patient is desired.

SUMMARY OF THE INVENTION

In one form, an improved fluid delivery system benefits from aclosed-loop control process that uses flow rate information to ensurethat the desired flow rate is substantially achieved. Further, in oneform, such a system is constructed using one or more micro-fabricationand/or molding techniques allowing for a cost-effective, disposableadministration set.

Briefly described, a system for delivering fluid at a desired flow ratefrom a reservoir to a delivery point associated with a patient,embodying aspects of the invention, includes a delivery channel betweenthe reservoir and the delivery point through which the fluid isdelivered to the patient. A pump is associated with the delivery channelfor operatively delivering the fluid to the delivery point at anadjustable output rate. A flow sensor is located along the deliverychannel for sensing a flow of the fluid in the delivery channel and forgenerating a flow rate signal indicative of a rate of flow of the fluidin the delivery channel. The flow sensor comprises a positivedisplacement flow sensor. A controller controls the pump. The controllercauses adjustments to the output rate of the pump as a function of theflow rate signal whereby the desired flow rate is substantiallyachieved.

In another aspect, the invention relates to a closed-loop fluid deliverysystem for delivering a fluid from a reservoir to a delivery pointassociated with a patient at a desired delivery rate via anadministration tube. The closed-loop fluid delivery system includesfluid delivery means located along the administration tube foroperatively supplying the fluid to the delivery point at a controllableoutput rate. A positive displacement flow sensing means is locatedbetween the fluid delivery means and the delivery point for sensing anactual flow rate of the fluid in the delivery channel and for generatinga flow rate signal indicative of the actual flow rate of the fluid inthe delivery channel. A control means associated with the fluid deliverymeans receives and is responsive to the flow rate signal for adjustingthe output rate of the fluid delivery means such that the desireddelivery rate at which the fluid is supplied to the delivery pointassociated with the patient is substantially achieved.

In still another aspect, the invention relates to a system fordelivering a fluid from a reservoir to a delivery point associated witha patient at a desired delivery rate via an administration tube. Thesystem includes a delivery mechanism operatively connected between thereservoir and the delivery point. The delivery mechanism is constructedand arranged for selectively delivering the fluid to the delivery pointvia the administration tube at a controllable output flow rate. Aclosed-loop control system controls the output flow rate of the deliverymechanism. The closed-loop control system includes a positivedisplacement flow sensor connected in-line with the administration tubefor determining an actual flow rate of the fluid in the administrationtube and for providing an flow rate indication reflecting the actualflow rate. A reader associated with the positive displacement flowsensor receives the flow rate indication and provides a flow controlsignal reflecting the flow rate indication. A controller associated withthe delivery mechanism receives and is responsive to the flow controlsignal for controlling the output flow rate of the delivery mechanism asa function of the flow control signal such that the output flow rate issubstantially equal to the desired delivery rate.

In yet another aspect, the invention relates to a method of delivering amedical fluid to a delivery point associated with a patient at a desireddelivery flow rate. The method includes operatively connecting areservoir to a delivery mechanism. The reservoir contains the medicalfluid to be delivered to the delivery point. The delivery mechanism isoperatively connected to an administration tube. The administration tubeis in fluid communication with the delivery point. The deliverymechanism receives the medical fluid from the reservoir and supplies themedical fluid to the delivery point via the administration tube at anoutput flow rate. The output flow rate of the medical fluid in theadministration tube is sensed using a positive displacement flow sensor.The sensed output flow rate of the medical fluid is compared with thedesired delivery flow rate. The delivery mechanism is controlled suchthat the output flow rate substantially corresponds to the desireddelivery flow rate.

In another aspect, the invention relates to a closed-loop flow controlsystem for controlling a medical fluid delivery system. The medicalfluid delivery system delivers a fluid from a reservoir to a deliverypoint associated with a patient at a desired delivery rate via anadministration tube. The medical fluid delivery system includes adelivery mechanism operatively connected between the reservoir and thedelivery point. The delivery mechanism is constructed and arranged fordelivering the fluid to the delivery point via the administration tubeat a controllable output flow rate. The closed-loop flow control systemincludes a positive displacement flow sensor connected in-line with theadministration tube for determining an actual flow rate of the fluid inthe administration tube and for providing an flow rate indicationreflecting the actual flow rate. A reader associated with the positivedisplacement flow sensor receives the flow rate indication and providesa flow control signal reflecting the flow rate indication. A controllerassociated with the delivery mechanism receives and is responsive to theflow control signal for controlling the output flow rate of the deliverymechanism as a function of the flow control signal such that the outputflow rate is substantially equal to the desired delivery rate.

In still another aspect, the invention relates to a method of detectinga blockage in a medical fluid delivery system arranged for delivering amedical fluid to a delivery point associated with a patient at a desiredflow rate. The method includes operatively connecting a reservoir to adelivery mechanism. The reservoir contains the medical fluid to bedelivered to the delivery point. The delivery mechanism is operativelyconnected to an administration tube that is in fluid communication withthe delivery point. The delivery mechanism receives the medical fluidfrom the reservoir and supplies the medical fluid to the delivery pointvia the administration tube at an output flow rate. The output flow rateof the medical fluid in the administration tube is sensed. Adetermination is made whether the sensed output flow rate is indicativeof a blockage in the administration tube. An alarm signal is provided ifit is determined that the sensed output flow rate indicates that theadministration tube is blocked.

In yet another aspect, the invention relates to an administration setfor use in connection with a fluid delivery system that is arranged fordelivering a fluid from a reservoir to a delivery point associated witha patient at a desired delivery rate. The fluid delivery system includesa pump having an output rate for delivering fluid from the reservoir tothe delivery point and a controller for adjusting the output rate of thepump such that the desired delivery rate is substantially achieved. Theadministration set includes an administration tube for providing fluidcommunication between the reservoir and the delivery point. A positivedisplacement flow sensor is located along the administration tube and issized and shaped for being positioned in fluid communication with thefluid within the administration tube. The positive displacement flowsensor senses a rate of flow of the fluid in the administration tube andgenerates a flow rate signal that is indicative of the sensed rate offlow of the fluid in the administration tube such that the controlleradjusts the output rate of the pump as a function of the flow ratesignal.

In another form, the invention relates to a positive displacement flowsensor for use in connection with a medical fluid infusion system thatincludes an administration set having an administration tube. Thepositive displacement flow sensor comprises a housing having an inletport and an outlet port. The inlet and outlet ports are operativelyconnected to the administration tube. A first rotor is positioned withinthe housing between the inlet port and the outlet port. A second rotoris positioned within the housing between the inlet port and the outletport. The second rotor is positioned adjacent to the first rotor, andthe first and second rotors are constructed and arranged to rotate inresponse to a flow of medical fluid in the administration tube fordetecting flow of the medical fluid in the administration tube. A coverencloses the housing such that when the medical fluid flows into theinlet port it causes the first rotor to rotate and thereafter themedical fluid exits through the outlet port.

Alternatively, the invention may comprise various other devices,methods, and systems.

Other objects and features will be in part apparent and in part pointedout hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates one embodiment of an infusion pump suitable for usein connection with aspects of the invention.

FIG. 2 is a block diagram of one embodiment of a closed-loop flowcontrol system suitable for use in connection with an medical fluidinfusion pump, such as the infusion pump of FIG. 1, according to aspectsof the invention.

FIG. 3A is a flow chart that illustrates an exemplary method ofdelivering a fluid to a patient in accordance with a closed-loop flowcontrol process, suitable for use in connection with aspects of theinvention.

FIG. 3B is a flow chart that illustrates an exemplary method ofdetecting and reporting a blockage/occlusion in an infusion system, inaccordance with aspects of the invention.

FIG. 4A is a schematic representation of a top view of one embodiment ofa flow sensor suitable for use in connection with a closed-loop flowcontrol system such as the system of FIG. 2.

FIG. 4B is a schematic representation of a side view of one embodimentof a flow sensor suitable for use in connection with a closed-loop flowcontrol system, such as the system of in FIG. 2.

FIG. 5 illustrates an exemplary process of manufacturing a positivedisplacement flow sensor using a high aspect ratio lithographic process.

FIG. 6 illustrates an exemplary process of manufacturing a positivedisplacement flow sensor using a deep reactive ion etching sequence.

FIG. 7 is a top view of a cap piece, suitable for use in connection witha positive displacement flow rate sensor, in accordance with aspects ofthe present invention.

Corresponding reference characters indicate corresponding partsthroughout the drawings.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring now to the drawings, FIG. 1 illustrates one embodiment of aninfusion pump 100 suitable for use in connection with aspects of thepresent invention. In the illustrated example, the infusion pump 100comprises a syringe-type infusion pump. Infusion pump 100 includes ahousing 102, a display screen 104, and a control panel 106. The controlpanel 106 and the display screen are used to enter set-point data foroperating infusion pump 100 and for monitoring the operation of pump100.

The infusion pump 100 also includes a syringe barrel 108 for holding amedical fluid to be administered. A barrel bracket 110 attaches thesyringe barrel 108 is attached to the housing 102. A movable syringedriver 112 is also attached to housing 102 and is positioned inengagement with a syringe plunger 114. A driving mechanism withinhousing 102 is constructed and arranged so that the movable syringedriver 112 can drive syringe plunger 114 into: (or out of) syringebarrel 108 in a controlled direction along barrel 108.

Operationally, a user loads a desired amount of the fluid to beadministered into syringe barrel 108. Syringe barrel 108 is mounted tohousing 102 via bracket 110 and plunger 114 is moved into positionwithin barrel 108. Infusion pump 100 is attached to a patient 120 (e.g.,a human patient or a veterinary patient) via a channel such as anintravenous PVC administration tube 122. The user enters the desiredadministration program on control panel 106 and infusion pump 100controls a movement of plunger 114 via driver 112 to deliver the fluidto the patient at a programmed delivery rate corresponding to theadministration program.

To this point, the description of infusion pump 100 and its operation inconnection with patient 120 has been generally in accordance with knowninfusion systems. In other words, fluid delivery is controlled in anopen-loop fashion-based on a desired set point without regard to actualflow rates. Line 124 diagrammatically illustrates a closed-loopinformation feedback path from a flow rate sensor 126 that is positionedfor detecting a flow rate in tube 122 at a point between infusion pump100 and patient 120. Closed loop control using such flow information ina feedback path is discussed in greater detail in connection with FIG.2. Also, and as also discussed in greater detail below, aspects of asensed flow information feedback system can be used for occlusiondetection instead of or in addition to flow rate control.

FIG. 2 is a block diagram that schematically illustrates one embodimentof a closed-loop flow control system suitable for use in connection withan medical fluid infusion pump, such as a volumetric or ambulatory typepump. It should be understood that a syringe pump does not “draw” from areservoir. Rather, as shown in FIG. 1, the plunger of a syringe pumpacts upon the reservoir to output fluid to the patient. For presentpurposes, such differences between a syringe type pumps and volumetricand ambulatory type pumps are not substantial, and aspects of theinvention may be employed with each of these types of infusion pumps.

In particular, FIG. 2 illustrates a fluid reservoir 202 connected to anadministration tube 204. Arrows 206 indicate that a fluid flows in theadministration tube 204 into the patient. Administration tube 204 isoperatively connected to an infusion pump system 208 that is positionedalong the administration tube 204. It should be understood that theposition of the infusion pump system 208 and the nature and type ofconnection between infusion pump 208 and administration tube 204 willoften depend, at least in part, on the particular type of infusion pumpused. In the illustrated embodiment infusion pump 208 includes a pumpingdelivery mechanism 210. As will be explained in more detail below, thereare a variety of pumping mechanisms that may be employed. For example,the pumping mechanism 210 may comprise a syringe driver driving asyringe plunger in a syringe-type infusion pump. For present purposes,it is sufficient to note that the pumping mechanism 210 iscontrollable/adjustable for controlling/adjusting a flow rate of thefluid within administration tube 204 to conform with a desired flowrate.

A flow rate sensor 212 is located in-line with administration tube 204and receives the fluid through pumping mechanism 210. The flow ratesensor 212 preferably includes an inlet port 214 and an outlet port 216.The inlet port 214 receives flowing fluid at the flow rate provided bypumping mechanism 210 and provides flowing fluid at its output port 216.In one embodiment, administration tube 204 comprises a plurality of IVtube pieces. A first piece of IV tube connects pumping mechanism 210 toinput port 214 and a second piece of IV tube connects output port 216 toa delivery point associated with a patient 220. Other flow sensingarrangements are possible. For example, flow rate sensor 212 could belocated entirely within the IV tube.

It should be understood that, in a typical continuous infusion pump,fluid runs from a reservoir to an access device through anadministration set flow rate may be measured at any convenient pointalong the path because the flow rate is the same—upstream or downstreamof the pump. For example, the flow rate in administration tube 204 ofFIG. 2 just below fluid reservoir 202 is equal to the flow rate at inputport 214, as. well as at output port 216. Some infusion pumps (e.g.,metering and discontinuous systems), however, fill a defined volume offluid from a reservoir, and thereafter pump that fluid out, over time,according to the delivery profile. Further, an amount of compliance mayexist within a disposable administration set. Therefore, in manyapplications there will be value in locating the flow rate sensordownstream of the pump, and closer to the patient.

In one embodiment, fluid reservoir 202, tube 204 and flow rate sensor212 comprise part of a disposable administration set that is mounted ininfusion pump system 208. It should be understood that a disposable setcould include a variety of components including, for example, valves(e.g., normally closed valves), specialized pumping complements, and thelike. Further, the set can include a reservoir; or the reservoir can beseparate and integrated with the set through a spike or otherconnection.

The flow rate sensor 212 provides an indication of an actual rate offlow within administration tube 204. In one embodiment, flow rate sensor212 is a positive displacement flow sensor for providing a flow ratesignal 224 representing the actual flow rate of fluid flowing inadministration tube 204. It is to be understood that there are a varietyof ways that flow rate sensor 212 could provide the flow rate signal224. For example, flow rate sensor 212 can be constructed such that avarying optical contrast or electrical signal is generated by the flowof fluid. Exemplary structures and methods for providing such a flowrate. Signal are discussed in greater detail below. Further, in oneembodiment, flow rate sensor 212 comprises a passive device, having noelectrical connections thereto.

A reader 230, such as an optical or electrical signal detector, isPreferably positioned adjacent flow rate sensor 212 such that it canreceive/detect flow rate signal 224. In turn, the reader 230communicates the detected flow rate signal 224 to a controller 232 via acommunication path. In particular, reader 230 receives flow rate signal224 from flow rate sensor 212 and supplies a flow-control signal 234 tothe controller 232. It should be understood that the flow control signal234 preferably provides substantially the same information as the flowrate signal 224 an indication of the actual flow rate of fluid in tube204. For example, in one embodiment, the flow control signal 234comprises one or more pulses. In such an embodiment, controller 232 isprogrammed to interpret each pulse as corresponding to a fixed volume offluid flowing through sensor 216. Accordingly, controller 232 candetermine the actual flow rate sensed in the administration tube as afunction of the number of pulses received from reader 230. In such anembodiment, an indication of the cumulative flow volume delivered isprovided by the number of pulses, and an indication of the instantaneousflow rate is determined by the time period of the pulses.

In one embodiment, the communication path between reader 230 andcontroller 232 comprises a wired communication channel 236 In anotherembodiment, the communication path comprises a wireless (e.g., IR, RF,and/or the like) communication channel 238. The wireless channel 238 maybe advantageous, for instance, in systems in which flow rate sensor 212and/or reader 230 are located at a distance from controller 232 and/orwhen physical connectivity is undesirable. One exemplary wirelesscommunication channel uses Bluetooth™ wireless technology. Bluetooth™ isa wireless specification from a trade association, Bluetooth SIG, Inc.In general, it is a low cost and low power specification, operating inthe unlicensed 2.4 GHz spectrum, and using spread spectrum frequencyhopping techniques.

The controller 232 is operatively connected for automaticallycontrolling pumping mechanism 210. This is illustrated schematically asa pump control signal 240 on line 242 between controller 232 and pump210. It should be understood that a wide variety of devices may serve ascontroller 232. For example, controller 232 may be embodied by aprocessor (e.g., a microprocessor or microcontroller), discrete logiccomponents, application specific circuitry, programmable logic devices,analog circuitry, or combinations thereof. Further a motor-based pumpcould be controlled by adjusting the motor rotation rate or a cycle timeassociated with the motor. If a certain type of MEMS-based pump isemployed. for example, control may be achieved by adjusting thefrequency of a piezo oscillation.

The system can also be configured to provide a status signal. Forexample, controller 232 provides a status signal, such as an alarmsignal 250, on a line 252 (and/or a wireless channel 256) to a statusmonitoring device 254. In one form, the status monitoring device 254comprises an audible alarm system for providing an audible alarm in theevent of a malfunction. Status monitoring device 254 may also compriseother audio, visual, audio-visual, and vibrating devices such as, forexample, CRT monitors, pagers, horns, buzzers, speakers, computers,portable telephones (e.g., cellular telephones), personal digitalassistants (PDAs), and the like. By way of one specific example,controller 232 provides an alarm signal to cause an audible and/orvisual alarm to be activated if controller 232 is unable to control pump210 to achieve a desired flow rate. Such a condition can occur if anocclusion or blockage in administration tube 204 prevents an adequateflow of fluid to patient 220. Such a blockage may include completeblockages, as well as partial blockages affecting flow rate. Alarmconditions can be programmed to occur for a variety of other reasons,such as when the fluid supply in reservoir 202 becomes depleted to alevel at which pump 210 can no longer deliver the fluid at the desireddelivery rate. It should be appreciated, however, that statusindications other than failures or improper operational conditions mayalso be provided. For example, a status signal could be used to providean indication at a remote monitoring station of the current sensed flowrate or another indication regarding the operation of the system.Similarly, sensed flow rate information can be used to anticipate whenthe fluid supply will be depleted, such that a suitable indication isprovided in advance of such event.

An operational example of the closed-loop flow control system of FIG. 2is now described. A patient is operatively connected to administrationtube 204 (e.g., via a catheter inserted at a desired delivery pointassociated with the patient). Reservoir 202 contains a fluid to beadministered to the patient and is operatively connected toadministration tube 204 and pumping mechanism 210. A desired deliveryrate is entered on a control panel associated with the pump (see, e.g.,FIG. 1). In FIG. 1, for example, it is to be understood that controlpanel 106 and display 104 cooperate to provide a user interface tofacilitate entering set-point data for use by pump 100. In the presentembodiment, controller 232 uses set-point data representative of thedesired delivery rate in combination with the flow control signal 234far controlling the system.

As pump 210 causes the fluid to be delivered to patient 220 via tube204, flow rate sensor 212 senses the flow rate of the fluid in tube 204and periodically (or continuously) outputs flow rate signal 224 which isreceived/detected by reader 230. For example, if flow rate sensor 212 isconstructed and arranged to provide an optical signal indication of theactual flow rate of fluid, reader 230 comprises an optical reader fordetecting the optical signal indication generated by flow rate sensor212. As a further example, in one embodiment reader 230 illuminates flowrate sensor 212 with a light and examines the light reflected by theflow rate sensor to determine the flow rate signal 224.

Reader 230 thereafter provides flow control signal 234 to controller232. This flow control signal 234 is functionally related to the flowrate signal 224 and, therefore, provides an indication of the actualflow rate of fluid into patient 220. As such, controller 232 is able tomonitor the actual flow rate of fluid in tube 204. With thisinformation, controller 232 is able complete a closed-loop control pathwith pump 210. In other words, controller 232 executes a control schemefor generating the pump control signal 240 to adjust the pumping actionof pump 210 so that the actual flow rate, as measured by flow ratesensor 212, more closely matches the desired flow rate. It should beunderstood that a variety of control schemes may be employed, dependingupon goals. For example, in some applications it may be desirable tocontrol the pump to provide a high degree of accuracy in terms ofinstantaneous flow rate. In other applications, it may be desirable tocontrol the pump in terms of the total volume of fluid infused. In stillother applications, it may be desirable to optimize control in terms ofboth instantaneous flow rate and total volume. Other variations arepossible.

The degree of accuracy with respect to controlling flow rate can bevaried, depending upon usage For example, if gross accuracy (e.g.,+/−15%) is acceptable, the closed-loop feedback control could bedisabled in software (e.g., via a control panel input) or by eliminatingflow rate sensor 212 from the administration set. Gross accuracy canalso be achieved by adjusting control parameters, such as sample ratesand so on. On the other hand, if a relatively high degree of accuracy isdesired (e.g., +/−2%), the controller is preferablyprogrammed/configured to tightly control the pumping action of pump 210.It should be appreciated, therefore, that an infusion pump system,embodying aspects of the invention can be reconfigured to accommodate awide variety of needs, thereby improving the usefulness of such asystem.

As explained above, such a closed-loop flow control system has beenheretofore unknown in the art. Among the advantages of such a system isthe ability to more closely control the flow of fluid to patient 220. Insome situations, a particular precise flow rate is valuable. Further,flow rate sensor 212 is compatible with a wide variety of fluid deliveryprofiles, including constant profiles, pulsatile profiles, and othertime-varying and non-uniform delivery profiles. With such profiles,including pulsatile flow profiles, the pump may need to ramp up and/ordown from its running rate faster than with other delivery profiles.Thus, knowledge of actual flow rate helps to ensure tighter control ofthe profile. For example, controller 232 can monitor the actual flowrate in tube 204 (as detected by flow rate-sensor 212) over time andcontrol the pumping action of pump 210 to ensure that the actual flowrate conforms to the desired delivery profile. Moreover, closed-loopcontrol allows infusion pumps to be manufactured with a greater degreeof flexibility in terms of manufacturing tolerances and the like. Insome prior art systems, delivery accuracy is attempted by tightlycontrolling the tolerances of the mechanical pumping components andmechanisms, which can be expensive. With flow rate feedback controlaccording to aspects of the invention, on the other hand, infusion pumpscan be made with less precise (and therefore less expensive) componentsand mechanisms, yet still achieve a high degree of accuracy in terms offluid delivery rate control.

It should be further appreciated that the tubing would not need to be asprecise and the integration of the pump and disposable components wouldbe less dependent upon the materials used in. the disposable components.For example, PVC tubing provides certain advantages in prior artsystems, so the design of the infusion pump may need to be tailored tobe compatible with such tubing. This type of engineering expense may beeliminated if PVC tubing is no longer necessary.

Further, knowing the actual rate of flow in tube 204 with a relativelyhigh degree of precision also allows the system to provide a highlyaccurate and fast occlusion detection capability. If should beappreciated that a blockage a complete blockage and/or a partialblockage between the fluid reservoir and the delivery point can resultin an unacceptably low rate of flow. Such blockages are sometimesreferred to herein as occlusions but may be caused by a variety ofconditions, including a kink in tube 204. Prior art attempts to detectocclusions rely on pressure sensing, which requires a relatively largechange in the pressure in the tube to be detected. A disadvantage ofpressure sensing is that it may take a long time for the pressure in thetubing to increase to a detectable level. This is especially true whendelivering fluids at a relatively low delivery rate. For example, ablockage (e.g., a complete and/or partial blockage) associated with a0.1 ml/hour delivery rate could take two hours or more to be detectedwith a typical prior art pump. Further, if the sensitivity of a pressuresensing system is increased to reduce response times, more false alarmsare likely to be experienced.

In contrast, a closed-loop flow controller according to aspects of thepresent invention is able to rapidly detect blockages (complete and/ornon-complete blockages, even at very low delivery rates) because flowrate sensor 212 detects an actual flow rate and does not require apressure build up. One embodiment of flow rate sensor 212 is capable ofproviding accurate measurements (e.g., better than +/−5%)—over four logsof range. For example, a pump using such a flow sensor supplies fluidfrond about 0.1 ml/hr up to about 2000 ml/hr. Thus, flow rate sensing.and occlusion detection is possible at low-flow rates, as well as athigher flow rates.

For convenience, the foregoing descriptions of FIGS. 1 and 2 have beengenerally provided in terms of embodiments comprising syringe-typeinfusion pumps and ambulatory and volumetric pumps. One type of priorart syringe pump is more fully described-in commonly assigned. U.S. Pat.No. 5,533,981. It should be understood that, with the benefit of thepresent disclosure, closed loop control systems and methods may beadapted for use with other types of medical fluid delivery systems. Suchsystems include, for example, rotary and linear peristaltic-type pumpsystems, valve-type pump systems, piezoelectric pump systems,pressure-based pump systems, and various motor and/or valve drivensystems.

A peristaltic-type pump manipulates the IV administration tube toachieve a desired flow rate. In one embodiment, a peristaltic-type pumpemploys an array of cams or similar devices that are angularly spacedfrom each other. The cams drive cam followers that are connected topressure fingers. These elements cooperate to impart a linear wavemotion on the pressure fingers to apply force to the IV tube. This forceimparts motion to the fluid in the IV tube, thereby propelling thefluid. Other forms of peristaltic-type pumps use different pressuremeans such as, for example, rollers.

Some valve-type pumps employ pumping chambers and upstream anddownstream valving (e.g., electronically controlled valves) tosequentially impart a propulsion force to the fluid to be delivered tothe patient. It is also possible to use a valve in connection with agravity-fed delivery system in which gravity provides the motivatingforce and one or more valves are used to control the flow rate.Piezoelectric pumps control pumping by varying the magnitude of anapplied voltage step. Pressure-based pumps adjust flow rate bycontrolling the pressure applied to a fluid reservoir (sometimes called“bag squeezer” systems).

Further, the closed-loop control systems and methods described hereinmay be used in ambulatory infusion pump systems and volumetric infusionpump systems. It should also be understood that the componentsillustrated in FIG. 2 are grouped for Convenience. For example, thestatus monitor device 254 could be made integral with the rest of the,infusion pump system 208: Likewise, reservoir 202 could be integral withthe pump unit or Separate. For example, in a syringe pump, the barrel ofthe syringe acts as a reservoir, but is physically mounted to theinfusion pump housing. In other words, with syringe pumps andpressure-based pumps, the reservoir is typically contained within thepump boundaries. With a volumetric or ambulatory pump, the reservoir isgenerally more external to the pump boundaries.

FIG. 3A is a flow chart that illustrates an exemplary method ofdelivering a fluid to a patient in accordance with a closed-loop flowcontrol process. As illustrated therein, a fluid reservoir (e.g., afluid bag) is connected to an infusion pump which, in turn, is connectedto the patient (blocks 302, 304). After a desired delivery rate isselected (block 306), fluid delivery begins (block 308). Periodically.(or continuously) the actual flow rate of fluid to a delivery pointassociated with the patient is sensed. (block 310). For example, and, asexplained above, a positive displacement flow rate sensor locatedin-line between the patient and the pump can be used to sense actualfluid flow and provide a flow rate indication to a control device. Theactual flow rate is compared to the desired delivery rate at block 312.If the actual flow rate is appreciably greater than desired (block 314),the infusion pump is adjusted such that its output rate is reduced(block 316), thereby reducing the actual delivery rate to more closelymatch the desired flow rate. If, however, the actual flow rate isappreciably less than the desired rate (block 318), the infusion pump isadjusted such that its output rate is increased (block 320), therebyincreasing the actual delivery rate.

In one embodiment, the method also includes using a disposableadministration-set that includes, for example, an administration tubeand an in-line flow rate sensor (e.g., tube 204 and flow rate sensor 212of FIG. 2) such that, upon completing the fluid delivery process, theadministration set is discarded.

FIG. 3B is a flow chart that illustrates an exemplary method ofdetecting and reporting a blockage/occlusion in an infusion system, inaccordance with aspects of the invention. In the illustrated example,the process is similar in several aspects to the method illustrated inFIG. 3A. At block 330, however, the sensed actual flow rate is comparedto an occlusion/blockage threshold reference. This threshold tan be apredetermined valve (e.g., a Red number Or a fixed Percentage of thedesired delivery rate). Of a dynamically determined value (e.g., a timevarying threshold). In the illustrated embodiment, if the sensed actualflow rate is less than the occlusion threshold, a blockage is declaredand an alarm condition is. triggered (blocks 332, 334). It should beunderstood, however, that more complicated comparisons can also beperformed. For example, rather than comparing sensed flow rateinformation against a threshold flow rate value, a change in the sensedflowrate (e.g., a slope) can be determined. If the slope exceeds a slopethreshold, a blockage is declared. Further, there may be certaininfusion protocols in which zero flow is expected for extended periodsof time. In such situations, the controller preferably accounts for thisfact.

It should be appreciated that flow rate comparisons (e.g., block 314 orblock 330) need not be referenced to a fixed Value. Rather, other flowrate comparisons are possible. Such comparisons include comparing theflow rate to an acceptability range and/or a time varying reference.Further the reference to which the actual flow rate is compared may beprogrammed by the user or pre-existing and used in connection with analgorithm or treatment protocol.

FIGS. 4A and 4B are schematic representations of one embodiment of aflow rate sensor 402 suitable for use in connection with a closed-loopflow control system, such as the pump system 208 illustrated in FIG. 2.Flow rate sensor 402 preferably comprises a micro-fabricated MEMS deviceor a similar micro-molded device (e.g., an assembly of micro-moldedcomponents). Exemplary fabrication techniques for manufacturing such aflow sensor are discussed below. Flow rate sensor 402 has an inlet port404 and an outlet port 406 and is preferably constructed and arranged tofit in-line with an administration tube (e.g., tube 204 of FIG. 2) suchthat the fluid flowing in the tube to the patient also flows throughsensor 402.

In the illustrated embodiment, flow rate sensor 402 comprises a positivedisplacement flow sensor. In general, such sensors operate by allowingknown volumes of fluid to be transferred during each rotation. Theparticular flow sensor illustrated comprises a two inter-meshedgears/impellers 408, 410 (sometimes referred to herein as rotors orrotating members). In the illustrated example, each impeller has sixlobes, but other sizes and shapes may be used. As illustrated, theimpellers are held on pins. Within a housing 412. The housing ispreferably sized and shaped for being used in-line with anadministration tube (e.g., tube 204 of FIG. 2). In one embodiment, theflow sensor comprises four components: the first impeller 408; thesecond impeller 410; the housing (including the pins on which theimpellers are mounted and rotate); and a cover 416 sized and shaped forsealing the unit such that entry and exit Triust be had via inlet 404and outlet 406, respectively. The cover, housing, and impellers are alsopreferably sized and shaped such that substantially all fluid passingthrough the sensor passes by operation of first and second impellers 408and 410 in a positive displacement fashion.

The cover 416 may be clear so that the operation of the sensor maytie-monitored by an optical reader. If the flow sensor 402 isconstructed primarily out of a silicon or silicon-based material, cover416 preferably comprises a flat, clear, and heat resistant material,such as, for example Pyrex®. If flow sensor 402 is constructed primarilyout of plastic, a flat plastic cover may be used. Laser weldingtechniques or ultrasonic welding may be used to seal the cap to thebase. Preferably, in ultrasonic welding applications, energy directorsare also used.

By way of further example, the alignment pins that hold the impellers inplace could be part of the cap and/or the base. Further, the base and/orcap could include recessed holes to accept pins that are part of theimpellers (i.e., the impellers have pins that extrude from their top orbottom).

In operation, flowing fluid causes impellers 408, 410 to rotate and totransfer a known volume of fluid from the input port 404 side to theoutlet port 406 side. Optical or other techniques are used to countrotations (or partial rotations). Such information is indicative of flowrate because each rotation relates to a known volume of fluid.Therefore, flow rate sensor 402 effectively provides a flow rate signalthat is indicative of an actual rate of fluid flow through the sensor.

One method of providing an optical indication is to mark one or more ofthe lobes of one or both impellers 408, 410 such that an opticalcontrast is created. An optical reader then optically detects when themarked lobe has moved, thereby providing an indication of a rotation.Similarly, the reader may be configured to illuminate flow rate sensor402 (e.g., using an LED) and to thereafter examine the light reflectedto detect the output signal (e.g., flow rate signal from flow ratesensor 212 in FIG. 2). In optical detection approaches described herein,the flow sensor itself is preferably passive the reader supplies thelight and processes the returned light to provide a signal to thecontroller. A controller (e.g., controller 232) can use this informationto determine an actual flow rate through flow rate sensor 402. This isso because each rotation of the impellers' results in a known volume offluid passing through the impellers. FIG. 7, which is discussed ingreater detail below, illustrates one embodiment of a rotationalmeasurement technique that is particularly suited for use when the flowrate sensor uses a transparent plastic cap.

Other methods of detecting rotation are possible. For example, animpeller can include a magnetic component that generates a detectablemagnetic field that changes as the impeller rotates (e.g., an electricalvariation caused by the rotation of the impeller). Such a changingmagnetic field would provide a flow rate signal that could be detectedby, for example, a Hall sensor or similar device.

As another alternative, the reader may be made integral with the flowrate sensor itself. For example, a semiconductor device may be used(e.g., a semiconductor that forms or is part of the cap). The rotationrate is detected electronically by the semiconductor device and theoutput signal is provided directly to the controller, without the use ofa reader that is separate from the flow rate sensor.

In one embodiment, flow rate sensor 402 is constructed using relativelylow-cost, precision MEMS and/or micro-molding techniques so that thesensor can be used in connection with a cost-effective, disposableadministration set suitable for use in delivering a medical fluid. Thus,the components that do not come directly into contact with the fluidand/or patient (e.g., the pump, controller, and so on) are reusable,while the parts that come into contact with the fluid and/or patient aredisposable. In another embodiment, the administration set and infusionpump are both designed to be disposable (e.g., disposed after each use).Two exemplary manufacturing techniques are discussed in greater detailbelow. It should also be understood that other types of flow sensors andother positive displacement arrangements may be used, and that theillustrated flow rate sensor 402 is provided for exemplary purposes.For-example, other configurations of positive displacement flow sensorsmay use a different number of-lobes and/or impellers, or have impellersof varying sizes and shapes—including asymmetrical impellers.

FIGS. 5 and 6 illustrate two exemplary methods of manufacturing a flowsensor, such as flow rate sensor 402, suitable for use in connectionwith-aspects of the present invention. More particularly, FIG. 5illustrates the pertinent steps of manufacturing a positive displacementflow sensor using a high aspect ratio lithographic process which issometimes referred to herein as ultra-violet LIGA (UV LIGA) or deepultra-violet LIGA (DUV LIGA). FIG. 6 illustrates the pertinent steps ofmanufacturing a positive displacement flow sensor using a deep reactiveion etching sequence (deep RIE).

UV LIGA typically results in plastic parts. Deep RIE uses silicon orsilicon carbide. Thus, the materials base for each approach differs.Further, both processes may be used to manufacture parts. The UV LIGAapproach, however, may be more advantageously practiced if it is used tocreate replication masters that are used as molds or mold inserts.

Referring first to FIG. 5, generally stated, the UV LIGA approachcomprises four steps 502, 504, 506, and 508. Step 502 involvespreparation and exposure. Step 504 involves developing. Step 506involves electroplating. Step 508 involves removing any remainingphotoresist.

At step 502, a mask 510 (e.g., a quartz glass mask with chrome patterns)is placed above a workpiece to be exposed. The workpiece to be exposedcomprises a substrate layer 512 (e.g., a silicon wafer). Prior toexposure, a seed layer 514 is attached to the substrate 512 by adeposition process. A photoimageable material, such as an epoxy-basednegative photoresist layer 516 (e.g., SU-8) is added on top of substrate512 (e.g., deposited from a bottle and spin coated). The mask 510comprises a two-dimensional pattern that is subsequently transferreddown to the SU-8 layer. The seed layer 514 is typically nickel, gold,copper, or nickel-ferrite (NiFe). Below seed layer 514 there may also bea “flash” or very thin layer of a refractory metal such as chromium,titanium, Or tantalum to act as an adhesion layer. Typically, the flashlayer is on-the order of 50-500 A, and the seed layer is about 400:5000A. Additional information regarding this process may be found at Chapter5 of the “Handbook of Microlithography, Micromachining, andMicrofabrication, Volume 2 Micromachining and Microfabrication,”available from SPIE Press 1997. The photoresist layer is selectivelyexposed to deep UV radiation through the pattern of mask 510.

At step 504, the exposed photoresist layer 516 is developed. Thedeveloping solution is a solvent and generally depends on thephotoresist being used and whether the photoresist is a positive ornegative tone. This development process removes the portions ofphotoresist layer 516 that were exposed to the UV radiation, leavingstructures 530 and 532. At step 506, the remaining structureselectroplated (up from seed-layer 514), filling the exposed portions 536removed during the development process. At step 508, the remainingportions of the. photoresist (e.g., structures 530, 532) aredeveloped/etched away, leaving the electroplated structures 540, whichmay be lifted off of the wafer substrate.

It should be appreciated that a number of such electroplated structures540, of different sizes and shapes, could be simultaneously formed. Forexample, one structure could correspond to an impeller (e.g., impeller408 of FIG. 4A), and another structure could correspond to a housing(e.g., housing 412 of FIGS. 4A and 4B). These structures couldthereafter be assembled to form a flow sensor of an appropriate size andshape for use in connection with, for example, the various methods andsystems described herein. In other words, structures can be formed for aflow sensor housing having an inlet port and an outlet port, and havingpins for accepting first and second impellers. In one embodiment, aclear plastic cover is bonded to the top of the housing, therebyensuring that substantially all fluid flowing into the flow sensorthrough the inlet port exits the sensor through the outlet port.

It should also be appreciated that, rather than directly using theelectroplated structures 540 for construction a desirable flow sensor,the micro-fabrication processes described herein can be used forcreating molds or mold inserts (e.g., negative images of the desiredstructures). One advantage of such a micro-molding approach is that alarge number of molds can be made at once, thereby allowing forlarge-scale production of flow sensor components, without the need forusing the UV LIGA process other than for creating the mold. In oneembodiment, components may be made of a plastic or similar material thatis suitable for use in a medical environment (e.g., disposable). Forexample, numerous thermoplastic materials could be used (e.g.,polycarbonate or liquid crystal polymer) to mold flow sensors from themaster.

One advantage Of using UV-LIGA is that it does not require the use of anexpensive synchrotron radiation source. As mentioned above, there arerelatively few synchrotrons In the world. In contrast, UV sources aremore readily available and relatively inexpensive, and masters can becreated in most moderately equipped semiconductor clean roomenvironments.

Conventional synchrotron LIGA processes require X-Ray masks. These masksare fabricated by starting with standard quartz/chrome masks, with thedesired patterns thereon. The patterns are subsequently transferred ontosilicon (which is transparent to synchrotron radiation) in the form ofgold or beryllium patterns, which absorb radiation. DUV LIGA, incontrast, uses the standard quartz/chrome mask to directly process theSU-8. Therefore, another advantage of using UV LIGA is that the SU-8material and mask are believed to be less expensive than comparablematerials used in conventional synchrotron LIGA.

Referring next to FIG. 6, illustrated therein at 602, 604, 606, and 608,respectively, are pertinent steps associated with manufacturing apositive displacement flow sensor using a deep RIE micro-fabricationprocess. In general, deep RIE is a silicon-based process in which deepreactive ion etching is applied to selectively etch away siliconmaterial from the workpiece. The selectivity of the etching process isdetermined by photolithographic techniques, such as those developed formanufacturing integrated circuits. By its nature, deep RIE provides goodverticality, allowing 3-dimension structures to be established from2-dimension patterns.

Deep RIE provides a suitable process for manufacturing flow. sensors(either directly or by manufacturing micro-molds) for use in connectionwith a closed-loop flow control system and method, in accordance withaspects of the invention. One such flow sensor may be created etchingsilicon impellers-from one Substrate, and etching an accepting housingfrom another substrate (or from another part of a single substrate). Thehousing preferably includes alignment pins positioned for accepting theimpeller gears so that a positive displacement arrangement is formed.The housing also preferably includes a base having a landing. Theimpeller gears are then placed on their respective rotation pins (eithermanually or by an automated process). A coverslip (e.g., a clear, heatresistant cover material such as Pyrex® is thereafter anodically bondedto the landing on the base. All or part of the impellers and/or basesurface may be oxidized to produce a desired optical contrast betweenthe respective surfaces. This optical contrast can be used for Sensingrotation dale impellers.

FIG. 6 illustrates pertinent steps of producing an impeller and ahousing for a flow sensor. Beginning at 602, a workpiece is preparedcomprising a silicon substrate 612 bonded to a base layer 614. The baselayer 614 may comprise any number of materials. In one preferredembodiment, base layer 614 comprises another silicon wafer. This canalso be done with many different types of adhesive layers, andphotoresist may be used as an adhesive layer. Other substrate materialsmay be used such as, for example, silicon carbide. A photoresistmaterial 616 is applied on the silicon substrate and then patternedusing exposure and development steps. Thus, the photoresist is developedto form a 2-dimensional mask pattern so that etching selectively occursonly where desirable to create the part being produced. This pattern isthereafter transferred down into the base layer (e.g., silicon) usingreactive ion etching. Many commonly available photoresist materials aresuitable. It should be understood that the 2-dimensional mask patterncould be transferred to an alternate layer, such as a silicon nitride orsilicon oxide layer.

Further, a deposited metal could serve as the etch mask. Such a metallicetch mask would be useful in fabricating. relatively tall structures byreactive ion etching techniques. In the etching process, the base layer(e.g., silicon) may be etched at a higher rate than the photoresistlayer is being etched (e.g., perhaps 100 times greater). Thus, aphotoresist mask may-be rendered effective if the etching process iscarried-out extensively to fabricate tall structures (e.g., severalhundred microns deep). In fabricating such tall structures, a metallicetch-mask (etched even more selectively than a-photoresist) would beuseful.

Referring still to FIG. 6, the photoresist 616 has a 2-dimension shapecorresponding to the 3-dimension part being produced. For example, if animpeller is being produced, the photoresist has a 2-dimension shape likethat of the desired impeller. The workpiece is selectively exposed anddeveloped so that the exposed silicon is etched away, leaving the baselayer, a silicon structure of the desired height and shape, and thephotoresist (see 604). Thereafter, the photoresist is stripped away,leaving the base layer and the silicon structure (see 606). Finally, thestructure is released from the base. layer (see 608).

In one embodiment of a flow sensor (e.g., a positive displacement flowsensor) manufactured using deep RIE, the silicon parts are coated with arelatively harder material (e.g., silicon nitride, carbon, or diamond)before the sensor is assembled. Silicon is a hard, but brittle material.As such, a coating improves the strength and integrity of the parts.Also, it should be understood that, rather than manufacturing partsdirectly, deep RIE can be used to fabricate molds for micro-molding flowsensors in a relatively low-cost, high-volume manner.

In one embodiment, a micro-molded or micro-fabricated flow sensor (e.g.,a positive displacement flow sensor) is sized and shaped for beingplaced in-line with an administration tube (e.g., tube 204) as part of adisposable administration set. In another embodiment, such a flow sensoris integrated into an infusion set in which the fluid supply, the pump,the administration tube, the flow sensor, the controller and the readerare all part of a disposable unit.

Finally, although UV LIGA and/or deep RIE are believed to be twopreferred methods for manufacturing flow sensors (or molds therefor),other micro-fabrication techniques may be Substituted. These techniquesinclude, for example, synchrotron LIGA and techniques that are not yetavailable for exploitation.

FIG. 7 is a top view of a cap piece 700, suitable for use in connectionwith a positive displacement flow rate sensor, in accordance Withaspects of the present invention. As explained above, one, method ofdetermining flow rate using a positive displacement flow sensor (e.g.,Sensor 402 of FIGS. 4A and 4B) involves optically measuring the rotationof the impellers tubes. For example, a small optical spot is used tomark one of the lobes. A reader detects when the marked lobe passes agiven point and can thereby detect the rotation rate of the impeller.Because the flow rate sensor is a positive displacement type sensor,knowledge of the rotation rate corresponds to the actual flow rate. Asimilar technique involves a detector focused down, into the sensor,that looks for a reflection due to an optical contrast between the baseand impeller. If the base is dark and the impeller is relatively lightin contrast to the base, most of the reflected light will occur when alobe passes. Such an approach generally allows a faster detection ratethan monitoring a marked lob.

FIG. 7 illustrates an alternative to using an optical spot. Asillustrated, the cap piece 700 has imposed thereupon a pattern 702 thatreplicates one position of the two impellers relative to each other. Inone embodiment, pattern 702 is applied to cap piece 700 with additiveprocesses or subtractive. creating a roughened surface. The pattern 702is selected to provide an optical contrast between pattern 702 and theimpellers 704. For example, if the impellers are a shade of white, theimposed pattern 702 is a dark shade. A relatively broad light source isapplied from above to illuminate the flow sensor. Light is reflectedback from the relatively light impeller lobes when the impellers areexposed from behind pattern 702. Thus, as the impellers rotate, theamount of light reflected back (e.g., to an optical detector) varies asa function of the amount of the impeller 704 that is exposed from underpattern 702. Thus, reflection intensity will rise and fall to denoteeach partial rotation associated with a lobe. For example, the reflectedlight intensity will increase/decrease at a known number of cycles perrevolution, depending upon the number of lobes, thereby providing anindication of the rotation rate of the sensor. Such an approach allows aless precise optical system to be used because the entire filed may beilluminated.

It is to be understood that the steps described herein are not to beconstrued as necessarily requiring their performance in the particularorder discussed or illustrated. It is also to be understood thatadditional or alternative steps may be employed. It should be furtherappreciated that the novel principles and processes disclosed herein arenot limited to the particular embodiments illustrated and described. Forinstance, flow sensors having a “dual layer” nature can be fabricated(e.g., impellers having pins on the bottom). As a more particularexample, impellers having pins fabricated on the bottom can befabricated using DUV LIGA by adding another layer (i.e., anotherSU-layer after step 506), and thereafter, exposing, developing, andelectroplating. It is also possible to reverse the order fabricate pinsfirst and impellers second. Similarly, silicon etching can be used toetch the impellers (or pins). Thereafter, turn the wafer is turned overand attached to a base etch pins (or impellers).

Further, traditional machining fabrication techniques may be employed inconnection with aspects of the present invention. In particular,machining can be used in connection with DUV LIGA processing tofabricate features of a mold that are not dimensionally critical. Suchfeatures may include, in some embodiments, input and output ports of apositive displacement flow sensor. Similar, in fabricating flow sensorsusing silicon, a silicon package (e.g., the silicon components and coverslip) can be formed to fit inside a plastic housing that is fabricatedby traditional plastic fabrication techniques. Such a plastic housingcan include, for example, input and output ports. Other variations arepossible.

In view of the above, it will be seen that the several objects of theinvention are achieved and other-advantageous results attained.

When introducing elements of the present invention or the preferredembodiment(s) thereof, the articles “a”, “an”, “the”, and “said” areintended to mean that there are one or more of the elements. The terms“comprising”, “including”, and “having” are intended to be inclusive andmean that there may be additional elements other than the listedelements.

As various changes could be made in the above constructions and methodswithout departing from the scope of the invention, it is intended thatall matter contained in the above description or shown in theaccompanying drawings. Shall be interpreted as illustrative and not in alimiting sense.

1. A system for delivering a fluid at a desired flow rate from areservoir to a delivery point associated with a patient, the systemcomprising: a delivery channel between the reservoir and the deliverypoint through which the fluid is delivered to the patient; a pumpassociated with the delivery channel for operatively delivering thefluid to the delivery point at an adjustable output rate; a flow sensorlocated along the delivery channel for sensing a flow of the fluid inthe delivery channel and for generating a flow rate signal indicative ofa rate of flow of the fluid in the delivery channel, the flow sensorcomprising: a housing having an inlet port and an outlet port, the portsbeing operatively connected to the delivery channel; a first rotorpositioned within the housing between the inlet port and the outletport, wherein the flow rate signal is based directly on a rotation ofthe first rotor, the first rotor being arranged to rotate in response toa flow of medical fluid in the delivery channel, the first rotorincluding a marker indication; and a cover enclosing the housing suchthat when the medical fluid flows into the inlet port it causes thefirst rotor to rotate and thereafter the medical fluid exits through theoutlet port, the cover having a transparent portion adjacent to thefirst rotor that enables rotation of the marker indication to beoptically detected; and a controller for controlling the pump, thecontroller causing adjustments to the output rate of the pump as afunction of the flow rate signal whereby the desired flow rate issubstantially achieved.
 2. A system as set forth in claim 1 furthercomprising a reader associated with the flow sensor and positionedadjacent the first rotor, the reader being constructed and arranged fordetecting the rotation of the first rotor and for providing the flowrate signal as a function of the detected rotation of the first rotor.3. A system as set forth in claim 2 wherein the reader is positionedsubstantially within the cover.
 4. A system as set forth in claim 2wherein the reader comprises a Hall sensor that senses an electricalsignal caused by a rotation of the rotors and provides the flow controlsignal in response thereto.
 5. A system as set forth in claim 2 whereinthe reader comprises a light source.
 6. A system as set forth in claim 1wherein the cover comprises a generally transparent cover allowing lightto pass through a portion of the cover.
 7. A system as set forth inclaim 6 wherein the first rotor comprises a plurality of lobes, at leastone of the lobes being marked with the marker indication.
 8. A system asset forth in claim 6 wherein the cover has a substantially opaquepattern imposed thereon that substantially prevents light from passingthrough the pattern.
 9. A system as set forth in claim 8 wherein thepattern imposed on the cover corresponds to a shape and size of thefirst rotor.
 10. A system as set forth in claim 1 wherein the pump is aperistaltic pump, a piezoelectric pump or a valve pump.
 11. A system asset forth in claim 1 wherein the controller provides a closed-loopcontrol path with the pump.
 12. A system for delivering a fluid at adesired flow rate from a reservoir to a delivery point associated with apatient, the system comprising: a delivery channel between the reservoirand the delivery point through which the fluid is delivered to thepatient; a pump associated with the delivery channel for operativelydelivering the fluid to the delivery point at an adjustable output rate;a flow sensor located along the delivery channel, the flow sensorcomprising: a housing having an inlet port and an outlet port, the portsbeing operatively connected to the delivery channel; a first rotorpositioned within the housing between the inlet port and the outlet portand comprising a plurality of lobes, at least one of the lobes beingmarked with a marker indication the first rotor being arranged to rotatein response to a flow of medical fluid in the delivery channel; agenerally transparent cover enclosing the housing such that when themedical fluid flows into the inlet port it causes the first rotor torotate and thereafter the medical fluid exits through the outlet port;and a reader positioned adjacent the first rotor, the reader beingconstructed and arranged for detecting a rotation of the first rotorbased on an optical detection by optically detecting rotation of themarker indication and for providing a signal that is indicative of arate of the flow of the medical fluid in the delivery channel as afunction of the detected rotation of the first rotor; and a controllerfor controlling the pump, the controller causing adjustments to theoutput rate of the pump as a function of the flow rate signal wherebythe desired flow rate is substantially achieved.
 13. A system as setforth in claim 12 wherein the cover has a substantially opaque patternimposed thereon that substantially prevents light from passing throughthe pattern.
 14. A system as set forth in claim 13 wherein the patternimposed on the cover corresponds to a shape and size of the first rotor.15. A system as set forth in claim 12 wherein the reader comprises alight source.
 16. A system for delivering a fluid at a desired flow ratefrom a reservoir to a delivery point associated with a patient, thesystem comprising: a delivery channel between the reservoir and thedelivery point through which the fluid is delivered to the patient; apump associated with the delivery channel for operatively delivering thefluid to the delivery point at an adjustable output rate; a flow sensorlocated along the delivery channel for sensing a flow of the fluid inthe delivery channel and for generating a flow rate signal indicative ofa rate of flow of the fluid in the delivery channel, the flow sensorcomprising a rotatable impeller for rotating in response to the flow ofthe fluid in the administration tube, the flow rate signal comprising anoptical indication generated by a rotation of the rotatable impeller; anoptical reader, responsive to the optical indication, for receiving theflow rate signal and providing a flow control signal indicative of theflow rate signal, wherein the optical reader illuminates the flow sensorcausing a reflection from the rotatable impeller, wherein the opticalindication generated by the rotation of the rotatable impeller comprisesa variation in an intensity of the reflection from the rotation of therotatable impeller; and a controller for controlling the pump, thecontroller causing adjustments to the output rate of the pump as afunction of the flow rate signal whereby the desired flow rate issubstantially achieved.
 17. A system as set forth in claim 16, whereinthe system further comprises a housing disposed around the rotatableimpeller, the housing and the rotatable impeller each comprising apattern, wherein the housing pattern corresponds to the rotatableimpeller pattern, and the housing pattern provides an optical contrastto the rotatable impeller.
 18. A system as set forth in claim 16,wherein the rotatable impeller comprises a plurality of lobes.
 19. Asystem as set forth in claim 16, wherein the system further comprises awireless communication channel between the optical reader and thecontroller, the controller receiving the flow control signal via thewireless communication channel and causing adjustments to the outputrate of the pump in response thereto.
 20. A system as set forth in claim16, wherein the pump is a peristaltic pump, a piezoelectric pump or avalve pump.
 21. A system as set forth in claim 16, wherein thecontroller provides a closed-loop control path with the pump.